More officials are being used to implement child benefit cuts than chase down wealthy tax cheats, Labour said ahead of the introduction of the change.
Treasury answers to parliamentary questions showed 475 staff would be required from January to administer the removal of payments from higher-earning parents at a cost of almost £12 million.
They were also expected to be diverted from other areas as the Government had said it was not recruiting new staff to deal with the change, the Opposition said.
By contrast, an HM Revenue and Customs' "Affluent Unit" tasked with ensuring full tax was recouped from the richest individuals had only 300 staff, it added, and an "Offshore Co-ordination Unit" of 100.
Under the new rules, families where one parent earns between £50,000 and £60,000 will have their benefit reduced on a sliding scale, and stand to lose the benefit completely when a parent is earning over £60,000.
Shadow chief secretary Rachel Reeves said: "This is yet more evidence of the chaotic way in which this complicated and unfair change is being implemented.
"It's shocking that HMRC is employing more staff to take money from hard-working parents than it does to clamp down on offshore tax avoidance and evasion.
"It's now clear David Cameron and George Osborne did not think through this policy before they announced it.
"How can it be fair that single earner families on £50,000 will see their child benefit cut, while some couples earning as much as £100,000 will be able to keep theirs and people on over £150,000 actually get a tax cut?"